Bug#18761: constant expression as UDF parameters not passed in as constant

The code that set up data to be passed to user-defined functions was very
old and analyzed the "Type" of the data that was passed into the UDF, when
it really should analyze the "return_type", which is hard-coded for simple
Items and works correctly for complex ones like functions.
---
Added test at Sergei's behest.


mysql-test/r/udf.result:
  Verify that various arguments work.
  ---
  Added test at Sergei's behest.
mysql-test/t/udf.test:
  Verify that various arguments work.
  ---
  Added test at Sergei's behest.
sql/item_func.cc:
  For function-Items, test whether it is constant and set the struct members 
  for the UDF parameter appropriately.
  
  Replace tabs with spaces in affected code.
sql/udf_example.c:
  Include a simple function that is useful in testing.

2 files changed, 65 insertions, 27 deletions

diff --git a/sql/item_func.cc b/sql/item_func.cc
index a294bbd7a71..8e6b4d82b1d 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -2683,39 +2683,47 @@ udf_handler::fix_fields(THD *thd, Item_result_field *func,
     char *to=num_buffer;
     for (uint i=0; i < arg_count; i++)
     {
-      f_args.args[i]=0;
+      /*
+       For a constant argument i, args->args[i] points to the argument value. 
+       For non-constant, args->args[i] is NULL.
+      */
+      f_args.args[i]= NULL;         /* Non-const unless updated below. */
+
       f_args.lengths[i]= arguments[i]->max_length;
       f_args.maybe_null[i]= (char) arguments[i]->maybe_null;
       f_args.attributes[i]= arguments[i]->name;
       f_args.attribute_lengths[i]= arguments[i]->name_length;
 
-      switch(arguments[i]->type()) {
-      case Item::STRING_ITEM:			// Constant string !
+      if (arguments[i]->const_item())
       {
-	String *res=arguments[i]->val_str(&buffers[i]);
-	if (arguments[i]->null_value)
-	  continue;
-	f_args.args[i]=    (char*) res->ptr();
-	break;
-      }
-      case Item::INT_ITEM:
-	*((longlong*) to) = arguments[i]->val_int();
-	if (!arguments[i]->null_value)
-	{
-	  f_args.args[i]=to;
-	  to+= ALIGN_SIZE(sizeof(longlong));
-	}
-	break;
-      case Item::REAL_ITEM:
-	*((double*) to)= arguments[i]->val_real();
-	if (!arguments[i]->null_value)
-	{
-	  f_args.args[i]=to;
-	  to+= ALIGN_SIZE(sizeof(double));
-	}
-	break;
-      default:					// Skip these
-	break;
+        if (arguments[i]->null_value)
+          continue;
+
+        switch (arguments[i]->result_type()) 
+        {
+        case STRING_RESULT:
+        case DECIMAL_RESULT:
+        {
+          String *res= arguments[i]->val_str(&buffers[i]);
+          f_args.args[i]= (char*) res->ptr();
+          break;
+        }
+        case INT_RESULT:
+          *((longlong*) to)= arguments[i]->val_int();
+          f_args.args[i]= to;
+          to+= ALIGN_SIZE(sizeof(longlong));
+          break;
+        case REAL_RESULT:
+          *((double*) to)= arguments[i]->val_real();
+          f_args.args[i]= to;
+          to+= ALIGN_SIZE(sizeof(double));
+          break;
+        case ROW_RESULT:
+        default:
+          // This case should never be chosen
+          DBUG_ASSERT(0);
+          break;
+        }
       }
     }
     thd->net.last_error[0]=0;
diff --git a/sql/udf_example.c b/sql/udf_example.c
index 2fa7474eb16..a4f7eddd302 100644
--- a/sql/udf_example.c
+++ b/sql/udf_example.c
@@ -165,6 +165,9 @@ void avgcost_reset( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char *error
 void avgcost_clear( UDF_INIT* initid, char* is_null, char *error );
 void avgcost_add( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char *error );
 double avgcost( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char *error );
+my_bool is_const_init(UDF_INIT *initid, UDF_ARGS *args, char *message);
+char *is_const(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long
+               *length, char *is_null, char *error);
 
 
 /*************************************************************************
@@ -1075,4 +1078,31 @@ char *myfunc_argument_name(UDF_INIT *initid __attribute__((unused)),
   return result;
 }
 
+
+
+my_bool is_const_init(UDF_INIT *initid, UDF_ARGS *args, char *message)
+{
+  if (args->arg_count != 1)
+  {
+    strmov(message, "IS_CONST accepts only one argument");
+    return 1;
+  }
+  initid->ptr= (args->args[0] != NULL) ? 1 : 0;
+  return 0;
+}
+
+char * is_const(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long
+                *length, char *is_null, char *error)
+{
+  if (initid->ptr != 0) {
+    sprintf(result, "const");
+  } else {
+    sprintf(result, "not const");
+  }
+  *is_null= 0;
+  *length= strlen(result);
+  return result;
+}
+
+
 #endif /* HAVE_DLOPEN */